77667f4844
Follow up #40736 Clean up `CodeBlockRenderer::Custom` related rendering per the previous PR [comment](https://github.com/zed-industries/zed/pull/40736#issuecomment-3503074893). Additional note here: 1. The `Custom` variant in the enum `CodeBlockRenderer` will become not useful since cleaning all code related to the custom rendering logic. 2. Need to further review the usage of code block `metadata` field in `MarkdownTag::CodeBlock` enum. I would like to have the team further review my note above so that we can make sure it will be safe to clean it up and will not affect any potential future features will be built on top of it. Thank you! Release Notes: - N/A